This application claims the priority of 102 49 905.5 filed in Germany on Oct. 22, 2002, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a combing ring for an opening roller of an open-end spinning arrangement, comprising at least two surface coatings, one applied on top of the other, of which the bottom one is a wear-resistant, harder coating, while the upper one is a less hard, but fiber-friendly coating having a maximum thickness of 5 μm.
Combing rings for opening rollers are exchangeable parts subject to high levels of wear which, up to the present, have always had to be replaced. Wear arises because the combing means or structure of the combing rings, usually needles or saw-teeth, engage with a fed sliver during the spinning process and thus release individual fibers from the sliver due to the high-speed rotation of the opening roller. The acceleration of the single fibers occurs hereby by means of the friction forces generated by the combing means, which in time results in wear of the combing means.
In order to keep the wear of the combing rings down to an acceptable level, modern combing rings, and in particular their combing structure, are usually provided with a wear-resistant nickel-diamond coating. The surface of the combing structure obtains a certain roughness, which has, however, proved itself in the processing of cotton fibers. For the processing of synthetic fibers, however, the nickel-diamond coating has proved to be too rough, causing damage to the fibers. Therefore, in processing synthetic fibers, the trend has been to apply either uncoated combing rings or combing rings having a chemical nickel coating. The life duration of such combing rings is, however, not sufficiently long.
In German published patent application DE 40 08 637 (corresponding U.S. Pat. No. 5,164,236) a combing ring of the above mentioned type is known, in which two different coatings are applied one after the other, which coatings have different functions. Firstly, a bottom coating, preferably a metal carbide coating, serves to prevent wear, while the subsequently applied coating, which is less resistant to wear, makes the surface of the combing ring smoother and protects the fiber material to be processed. In this case, a chemical, subsequent nickel-plating, having a coating thickness of between 3 and 5 μm, is involved.
In German published patent application DE 41 01 680 a non-generic combing ring is known, to which two coatings are applied, one after the other, which are both wear-resistant. The first coating consists preferably of tungsten carbide. The second coating consists preferably of chrome or titanium nitride, which is particularly applied in the PVD process and has a thickness of between 5 and 35 μm. PVD is the abbreviation for the commonly known expression Physical Vapour Deposition, a process which is, for example applied in the form of ion coating. The bottom coating is somewhat rougher, comprising microscopic valleys and peaks. The top coating is applied in such a way that it only thinly covers the peaks of the lower coating, while filling out the valleys to a great extent.
It is furthermore prior art to coat combing rings, which are intended for the processing of synthetic fibers, using only PVD coating technology. A coating of this type is very wear-resistant and permits significantly higher life durations in the case of processing synthetic material. These PVD coatings have the disadvantage, however, that the application of the coating does not occur evenly. Due to the nature of the process itself, defects occur in the coating, so-called droplets. These droplets form as bumps on the surface and result in a comparably rough surface, whereby the surface roughness is, however, less rough than that of the above mentioned nickel-diamond coating. The droplets are significantly softer than the usual surface layer generated by the PVD coating.
It is an object of the present invention to keep the known advantages of the PVD coating technology while creating an even more wear-resistant and fiber-friendly combing ring.
This object has been achieved in accordance with the present invention in that the bottom coating is applied as a PVD coating comprising the above mentioned droplets, while the thickness of the top coating corresponds at least to the height of the droplets. The top coating is preferably a chemically applied nickel coating.
According to the present invention, the initially applied PVD coating, unsatisfactory due to the presence of the droplets, is covered by a further coating, the thickness of which does not exceed 5 μm, but which measures at a minimum the same as the height of the droplets. When the combing ring is in operation, the top coating, preferably a chemical nickel coating, comes into effect first during the run-in phase. In this phase the wear rate is very high, as the level of hardness of the top coating is very low. At the same time, the relatively soft droplets are worn away. After a run-in phase, the bottom PVD-coating comes into action. This now has an even, fiber-friendly surface and due to the high degree of hardness, also a high wear resistance.
These and further objects, features and advantages of the present invention will become more readily apparent from the following detailed description thereof when taken in conjunction with the accompanying drawings wherein